Calcium-cobaltous phosphate catalyst



United States Patent 3,205,181 CALClUlld-CUBALTUUS PHGSPHATE CATALYSTRobert S. Bowman and James M. Dixon, Pittsburgh, Pa.,

assiguors to The liaugh Chemical Company, Baltimore, Md, a corporationof Maryland No Drawing. Filed Feb. 28, 1963, Ser. No. 261,828

3 Claims. (Cl. 252-437) During recent years there has been a growingneed for an effective catalyst for converting saturated or partiallysaturated heterocyclic nitrogen compounds into heterocyclic nitrogencompounds of lower hydrogen content. Typical examples are the conversionof methyl and ethylpiperazine to, respectively, methyl andethylpyrazine, and of ethylpyrazine to vinylpyrazine. Other examplesinclude the conversion of piperidine or alkylpiperidines to theircorresponding pyridines, and or": alkylpyridines where the alkyl groupcontains two or more carbon atoms to vinylpyridines.

Conventional hydrocarbon dehydrogenation catalysts have seriousshortcomings when it is attempted to apply them to the foregoingpurposes. For example, unlike their hydrocarbon analogues, theheterocyclic nitrogen compounds are subject in the presence of steam tohydrolytic side reactions which can seriously impair catalystefliciency. Likewise, conventional catalysts for hydrocarbondehydrogenation when used for that purpose with heterocyclic nitrogencompounds, such as those named above, show less activity and lessselectively than is desired for efiicient and economical use.

It is among the objects of this invention to provide a method ofdehydrogenating heterocyclic nitrogen compounds which is simple; isapplicable to saturated and partially saturated compounds of this class;is easily practiced with standard, readily available equipment; is ofcommercially desirable activity and selectivity; and makes use of aneasily prepared catalyst of simple composition.

A further object is to provide a method in conformity with the foregoingobject which is applicable not only to the ring dehydrogenation ofheterocyclic nitrogen compounds to convert them to lower hydrogencontent but also to the production of vinyl heterocyclic compounds byside chain dehydrogenation.

Yet another object is to provide a novel dehydrogenation catalyst ofsimple composition which is easily prepared, which is especially adaptedto dehydrogenation of heterocyclic nitrogen compounds, and whichpossesses desirable activity and selectivity for that purpose.

Other objects will appear from the following specification.

Specifically, we have discovered that certain cobaltcalcium phosphatesare particularly well adapted for catalyzing the dehydrogenation ofheterocyclic nitrogen compounds of the types mentioned above. The uniqueproperty of the cobalt-containing calcium phosphates of this inventionwill be illustrated by the following data.

The invention may be exemplified in the first instance by the catalyzeddehydrogenation of ethylpyrazine to vinylpyrazine. In this study amixture of ethylpyrazine and water vapors was led, at about atmosphericpressure, through a 100 cc. bed of 7 catalyst pills in accordance withthe present invention contained in an externally heated, stainless steelreactor tube of 17 inside diameter. An ethylpyrazine-water mole ratio ofone to nine, at a total space velocity of 3900, was maintained bypumping a solution of ethylpyrazine in water onto a spiralvaporizer-preheater, mounted above the catalyst bed, using a precision,calibrated pump. Space velocity is defined as liters of vapor atreaction temperature per liter of catalyst bed volume per hour. Thecalculated average residence time under these conditions then is 0.92sec- Patented Sept. 7, 1965 end. The linear velocity is approximately4%. inches per second. The temperature, usually in the 550-650 C. range,was measured at a point about one-third from the bottom of the 4% highcatalyst bed.

The vapors emerging from the reactor tube were condensed in a spiraltype, cold-water condenser. The condensed material was weighed, thensaturated with potassium hydroxide which caused the organic material toseparate as a distinct oil layer. This oil layer was separated, weighedand then analyzed by gas chromatography. The percent vinylpyrazinecontent was noted. The liquid selectivity was then calculated bydividing percent vinylpyrazine by the sum of the percent vinylpyrazine,percent methylpyrazine, and percent pyrazine. These latter compounds arefound to be the chief byproducts of dehydrogenation of this compoundwith our catalysts. Thus, the vinylpyrazine content of the liquidorganic product will reflect catalyst activity, while the amounts ofby-product methylpyrazine and pyrazine will be indicative of catalystselectivity. Most of the runs were made over eight hour periods, afterwhich the catalyst was steamed for a short period of time, thenairstearned for one-half to one hour to regenerate the catalyst, andthen steamed for an hour or two. Data illustrative of the results ofsuch a procedure are set forth in tables appearing hereinafter.

The preparation of eilective cobalt-calcium phosphate catalysts can becarried out by either a co-precipitation technique, or by ion exchange,using an appropriate calcium phosphate. Typical examples will nowfollow. In the co-precipitation method, as, for example, in catalyst 304(Table I), 40 g. of cobaltous carbonate (CoCO are dissolved in 500 g. ofdilute, aqueous ortho phosphoric acid solution (H PO containing g. of P0 The resulting, clear, purple solution is then added slowly with goodstirring to 180 g. of calcium hydroxide suspended in about 2000 g. ofwater. The rate of addition of the acid solution should be such that thesuspension of Ca(OI-I) remains alkaline. The resulting slurry is thenstirred for one hour, then air-dried at C. The dried product, acobaltous calcium phosphate, is pulverized, and then calcined at 650 C.for one hour. The product is then pelletized, and then calcined againfor one hour at 650 C. after which it is charged to the dehydrogenationreactor. Bulk densities in the range of 0.6-0.8 g. per cc. are obtainedby this method.

In the ion exchange technique, as in catalyst 415 (Table II), thecalcium phosphate is first prepared by the slow addition of 500 g. ofdilute, aqueous phosphoric acid solution (H PO containing 100 g. of P 0to a wellstirred aqueous slurry of 180 g. of calcium hydroxide in 2000g. of water; the rate of addition should in this case also be such thatthe slurry remains alkaline. The resulting product slurry is stirred forabout an hour, after which a water solution of 84 g. of water solublecobaltous chloride hydrate is added. The mixture is stirred for severalhours, after which it is suction filtered and water washed until theabsence of chloride ion in the filtrates is established. The productcake is air-dried, and then processed as above for catalyst 304.

The cobalt content of these two catalysts, calculated as cobaltous oxide(C00), is 10.2 weight percent for catalyst 304, and somewhat less thanthis value for cata lyst 415 in the production of which a small amountof unexchanged cobalt salt was lost in the wash waters.

The calcium phosphates are defined in terms of Ca0- P O weight ratios.Thus, a ratio of 1.18 describes tricalcium phosphate, and a 1.32 ratiodescribes calcium hydroxyapatite. Ratios above 1.32 allude to morealkaline, or basic, calcium phosphates, while the more acidic, or lessbasic, members are found below 1.18. The two catalysts above aredesigned to have (CoO+CaO) to P ratios of 1.6, in which the calciumphosphate phase is a 1.36 CaOP O ratio material. In the presentinvention the basic calcium phosphates will be designated herein as BCP.

As shown in the following Table I it is of primary importance to avoidexcess alkalinity in the catalyst. Thus, the mildly alkaline catalyst304 exhibits the best performance. Catalysts 308 and 332 which are morealkaline due either to the addition of KOH (308) or to using a higherratio BCP (312), are shown to be considerably less active and selectivethan catalyst 304. The commercially used dehydrogenation catalyst ofTable I, an alkaline promoted iron oxide type, as well as an alkalizedcupric oxide-BCP catalyst (286) are also shown to be less active andselective than catalyst 304. The acidic catalyst 348, the cobaltanalogue of dicalcium phosphate, is likewise characterized by poorperformance. It follows that neutral to mildly alkaline catalystsurfaces are preferred for the purposes of this invention.

Table I.Efiect of alkalinity on. catalyst performance in thedehydrogenation of ethylpyrazine ing in steam for two hours at 1200 F;the product showed the wild behavior attributable to cobalt oxide. Incatalyst 332, the moderate performance can be attributed to a partiallyoxidic character of the cobalt, which may be due to the use of a highratio BC? in a coprecipitation process resulting in some non-phosphaticcobalt compound.

Table H.Nature of cobalt species in active dehydrogenation. catalysts 1Prepared by ion exchange between 1.86 BOP and C001 no Furthermore,neither cobaltous phosphate nor BCP P t PD t possesses thedehydrogenation capability that is exhibited Composition Bed 55 53 bythe cobalt calcium phosphate of this invention. Thus, Catalyst Weight,percent i e py fg Table II-A shows the results obtained whenethylpyrazine 3, 52,; N y was treated with those two materials under theconditions described in connection with Table I and II. It is clear 60038 91 that cobaltous phosphate is almost without activity, and that the1.36 ratio BCP shows only moderate activity, 600 g 7 giving furtherevidence that the active component of the 304-type catalysts is a cobaltcalcium phosphate. 600 13 55 v 600 2 Table II-A 600 35 92 Percent 25 62Catalyst Bed temp, vinyl- Percent N 0. Composition C. pyrazino liquidCommercial cle- 4 in liquid selectivity hydrogenation 600 19 69 Organiccatalyst. 13.3% KOH product P Also of great importance is the state ofOXldaUOH Of 8EZE 83ZI I j 323 :18 g: the cobalt in the catalyst. Thedata 1n Table II, which 620 $7 1.36 BCP 628 20.0 89 follows, clearlyreveal the necessity of having the cobalt 4661i 645 5.0 82 in thecobaltous condition. This conclusion is supported by the method ofcatalyst preparation, and by X-ray diifraction analyses. Thus, whereasthe cobalt phosphate catalysts 304, 333, and 415 are effectiveethylpyrazine dehydrogenation catalysts, the cobalt oxide-containingcatalysts 336 (no phosphate) and 402 (cobaltic oxide) are completelyineffective. These two catalysts are wild in behavior, in that theorganic feed is converted to carbon and light gases, and no liquidorganic material appears in the reactor effluent. The X-ray analyses ofcatalysts 304, 402, and 415 show the typical calcium hydroxyapatitepattern. In addition, cobalt oxide, added at the black cobalt oxide C0 0to a pre-precipitated 1.36 BCP in catalyst 402, is clearly detected inthe X-ray pattern, and the composition showed no activity. The lessalkaline catalyst 333 is found to exhibit the typical X-ray pattern ofB-tricalcium phosphate. Catalysts 304 and 333 were prepared by thecoprecipitation technique described previously, while 415 was preparedvia ion exchange. Since these three catalysts possess only the calciumphosphate X-ray patterns as the major lines, it is evident that cobaltis incorporated into these calcium phosphates without causing a shift inthe X-ray patterns. The absence of cobalt oxide lines (above the tracelevel) supports the conclusion that these eifective catalysts are, infact, cobalt-calcium phosphates. Catalysts 336, was prepared by heatinga physical mixture of cobaltous acetate and calcium carbonate in air ona hot plate at about 200 C. to pyrolyze the acetate, followed by heat-Table IH Efiect of cobalt content upon. activity of cobalt phosphatedehydrogenation catalysts Percent co- Percent balt calcuvinyl- PercentCatalyst lated as Temp, C. pyrazine liquid CO0 by wt. in liquidselectivity product A1 l catalysts prepared by the (ac-precipitationmethod; all have 1.36 ratio BOP.

The data in the following Table IV reveal an optimum range for the CaOPO ratios in the calcium phosphate portion of the catalysts. Thus, theslightly acidic 1.0 ratios are almost as effective as the 1.15 and 1.36ratio materials (approximately tricalcium phosphate and calciumhydroxyapatite, respectively). Further increases in alkalinity, to 1.6ratio, produce marked decreases in the performance of the catalyst.Thus, it is shown that for the purposes of this invention calciumphosphates below a 1.6 CaO-P O ratio should be used.

Table IV.-Efiect of BCP ratio upon activity of cobaltcalcium phosphatedehydrogenation catalysts Further study of these coprecipitated calciumphosphate catalysts shows that we believe cobalt to be the mosteffective metal for use in this application. Thus, in Table V, the useof copper, cadmium, zinc, chromium, nickel, and iron produce catalystswhich are distinctly inferior to the cobalt-calcium phosphate catalysts,typified by catalyst 304.

Table V.C0mparis0n among metal oxide-BOP catalysts in thedehydrogenation of ethylpyrazine The ethylpyrazine-water mol ratio andspace velocity used in obtaining the data of Table I were used in theruns reported in Tables II and II-A to VI.

The removal of hydrogen from a saturated heterocyclic ring structuresuch as piperazine and the alkylpiperazines requires less drasticconditions than those for the removal of side-chain hydrogen from, forexample, et-hylpyrazine. However, we have discovered that thecobalt-calcium phosphate type catalyst of our invention is also veryeffective in catalyzing the ring dehydrogenation of the piperazines.Thus, as shown in the following Table VII, the cobalt-calcium phosphatecatalyst 304 is clearly superior to the nickel, copper, and ironphosphate-calcium phosphate catalysts. In this work a stainless steelreactor similar to that described above was employed. A water solutionof methylpiperazine containing one mole of methylpiperazine in 29 molesof Water was employed as the feed to the reactor. At a vapor spacevelocity of 4370, the residence time was calculated to be 0.79 second.The linear velocity was 5.6 inchesper second. Reaction periods up to 60hours have been employed with only moderate decreases in catalyticactivity. Catalyst regeneration is accomplished. by the steaming andairsteaming process described herein above. In this work, it was foundto be desirable to distill the entire reactor efiluent through a10-plate fractional distillation column until the organic waterazeotrcpes or steam distillates had een collected. The distillate thencan either be extracted with benzene, or saturated with KOH to removethe organic material. The constituents of the separated organic phaseare then determined quantitatively by gas chromatography. Liquidselectivity values are calculated by dividing the methylpyrazine X 100content by the sum of the methylpyrazine, low boiling amines, pyrazine,and higher boiling products.

Percent Percent metal resvinyl- Percent Catalyst ent calculated asTemp.,C. pyrazinoin liquid Table 'Vllr-Compar metal OMdE'ZBCP catalystsmetal Oxide y llquld selectlvlty m the dehydrogenation ofmethylpzperazine product 304 10.2% 000 600 33 91 Percent metal PercentPercent 12.8% CuO 000 32 82 calculated as BCP Temp, ntethylliquid 10.Cdom 600 28 90 Catalyst metal oxide ratio C. pyrazine selec- 9. 4% ZHO-600 27 91 by wt. in liquid tivity 10.6% CI'zO 600 21 90 product 11.7%N10 600 19 55 eas a a a 11.5 a l v0 90 9 35 68% Fe O 600 14. 67 304 102%565 90 95 331 11.7% NIO 1.36-"..- 500 S9 91 12.8% CnO- 1.36--." 515 53 1BCP ratio 1.05. 2 B01? ratio 0.9. 283 47% F8203 1 36 228 7 377 47% Fe O31.75 560 40 78 Further, a study of catalyst phases other than calciumphosphate reveals that calcium phosphate is markedly superior for thispurpose. Thus, in Table VI, a group of catalysts containing calciumsilicate (496), in which the cobalt was incorporated by ion exchange,and the aluminate, chromate, arsenate and borate compounds, as incatalysts 428, 434, 436, and 437, respectively, do not perform as wellas the calcium cobaltous apatite catalyst, 304.

Table VI .C0mparis0n among various cobalt compounds in thedehydrogenation of ethylpyrazine 1 Supported upon 1.30 BCP; 58% byweight.

To summarize, we have discovered that cobaltous calcium phosphatecatalysts prepared within the limits as described are singular-1yelfective for the side-chain (lower alkyl) dehydrogenation ofunsaturated heterocyclic compounds, such as ethylpiperazine andethylpyridine to form the corresponding vinyl compounds. This type ofcatalyst is also remarkably eitective in catalyzing ringdehydrogenations, such as in the conversion of piperazines andpiperidines to, respectively, pyrazines and pyridines. The catalyst hasalso demonstrated the ability to convert, in a single stage process,ethylpiperazine to vinylpyrazine. In addition to the reductions notedhereinabove the invention is applicable to other dehydrogenations ofheterocyclic nitrogen compounds, for instance to the conversion ofpiperidine and its derivatives to, respectively, pyridine andsubstituted pyridines, and to the conversion of pyrrolidene to pyrrole.All such compounds are of known usefulness by applying known organicchemistry reactions to produce a variety of other compounds useful assuch or as intermediates in making other compounds.

The utility of the invention along the lines just indicated is shown bythe following Tables VIII, IX and X.

Table VIII.Dehydr0genati0n of alkylpyridines Percent vinyl- Bcd temp.,pyridine Percent Catalyst N0. Alkyl pyridine C. in the liquid liquidselectivity organic product IX .Delzydr0genati0n of pipcridine Percentpyridine in the liquid organic product Percent liquid selectivityCatalyst No. Carrier Gas or Bed temp., diluent C.

X .Dehydr0gcnati0n 0f pyrrolidine Percen t pyrrole in the liquid organicproduct Percent liquid selectivity Bed ten1p., Catalyst No. C.

In the runs of Table VIII the feed rates Were as stated for Tables I andII.

In Table IX the feed rates were 0.5 g./1nin. of piperidine, 2.0 g./min.of Water, and in the case of benzene 2.4 g./min. Hence the feed in thecase of Water was 1 mol of piperidine to 20.5 mols of water, and in thecase of benzene it was 5.7 mols of benzene per mol of piperidine.

Similarly, the data of Table X were obtained using a feed rate of 0.5g./min. of pyrrolidine and 3.6 g./min. of water, or a mol ratio ofpyrrolidine to water of 1228.5.

From the foregoing data it will be realized that in the practice of theinvention such ope-rating details as the ratio of heterocyclic nitrogencompound to water or diluent vapor and bed temperature may vary Widelydepending upon, for example, the particular compound to bedehydrogenated and the catalyst.

In the practice of the invention the non-condensable gases, chieflyhydrogen, may be exhausted with a hood on the small or laboratory scalewhile in commercial operation this gas stream may be burned as fuel orpurified for other uses.

According to the provisions of the patent statutes, We have explainedthe principle of our invention and have illustrated and described Whatwe now consider to represent its best embodiment. However, We desire tohave it understood that, within the scope of the appended claims, theinvention may be practiced otherwise than as specifically illustratedand described.

We claim:

1. A calcium-cobaltous phosphate dehydrogenation catalyst consistingessentially of, analyticaly, by Weight, about 4 to 14 percent ofcobal-tous oxide and the remainder CaO and P 0 in Weight ratios rangingfrom CaO:P O equals 1:1 to CaO:P O less than about 1.6:1.

2. A catalyst according to claim 1, said CaO:P O ratio being about1.36:1.

3. A catalyst according to claim 1, the ratio CaO:P O being about 1.36:1and the ratio (CaO+CoO):P O being about 1.6: 1.

References Cited by the Examiner UNIT ED STATES PATENTS 1,882,712 10/32AndrussoW et al 252-437 2,291,609 8/42 Cobbs et a1 23-108 X 2,336,60012/43 Musther 260-6832 2,542,813 2/51 Heath 252-437 2,631,102 3/53Hubbard et al 23-109 X 2,938,874 5/60 Rosinski 252-437 2,967,156 1/61Talvenheimo 252-437 3,033,864 5/62 Britton et a1 260250 3,067,199 '12/62Langdon 260250 MAURICE A. BRINDISI, Primary Examiner. JOHN D. RANDOLPH,Examiner.

1. A CALCIUM-COBALTOUS PHOSPHATE DEHYDROGENATION CATALYST CONSISTINGESSENTIALLY OF, ANALYTICALY, BY WEIGHT ABOUT 4 TO 14 PERCENT OFCABALTOUS OXIDE AND THE REMAINDER CAO AND P2O5 IN WEIGHT RATIOS RANGINGFROM CAO:P2O5 EQUALS 1:1 TO CAO:P2O5 LESS THAN ABOUT 1:6:1.